1. Technical Field
The present invention relates to a wireless communication apparatus, and in particular, to one that is suitably applied to a method of transmitting a reference clock used for wireless data communication in a non-contact manner, together with power.
2. Related Art
As a method that transmits power to an information terminal apparatus, such as a cellular phone, for the sake of charging, there is a method that transmits power using electromagnetic induction in a non-contact manner, in addition to a method that transmits power through a metal contact, such as a connector. The method that transmits power in a non-contact manner can have no poor contact by abrasion or stain and can maintain a waterproof property of a case, compared with the method that transmits power through the metal contact.
In JP-A-9-103037, there is disclosed a method that transfers power control information through an electromagnetic induction coil for power transmission such that a feedback control of supplied power can be performed without impairing the advantages of non-contact power feeding. Further, in JP-A-2005-73350, there is disclosed a method that provides a coil for data communication separately from a coil for power transmission in order to implement an electric tool that can perform optimum charging according to the state of a charger.
Meanwhile, in JP-A-6-133476, there is disclosed a method that performs wireless data communication using an antenna separately from a non-contact power transmission device so as to enable data communication, without being restricted by a power transmission side.
However, in the method that transmits power in the non-contact manner for the sake of charging or the like, in order to transfer mass image data stored in the information terminal apparatus, such as a digital camera or a cellular phone with a camera, to a personal computer, a connector for wired communication, such as a USB, is required, and thus there is a problem in that the above method cannot cope with transmission of mass image data.
In the methods disclosed in JP-A-9-103037 and JP-A-2005-73350, data communication is performed through a power transmission device, such as an electromagnetic induction coil, and thus there is a problem in that high-speed data communication cannot be performed.
In the method disclosed in JP-A-6-133476, a wireless machine is merely provided alone separately from the non-contact power transmission device, and thus there is a problem in that costs, power consumption, and the size are increased.
Meanwhile, in order to perform transmission of mass data, it is necessary to provide a local oscillator for generating a reference clock on transmitting and receiving sides. Further, it is necessary to provide an automatic frequency adjusting circuit or an A/D converter for adjusting a shift in frequency of the reference clock on the transmitting and receiving sides. Accordingly, there is a problem in that the size of the circuit is increased.